This invention relates to a mail sorting system, more particularly, a mail sorting system provided with a plurality of mail sorters and coding devices.
Various types of automatic mail sorting devices have been proposed in order to save labor in mailing services. One known type of mail sorter is described, for example, in European Patent Application EP No. 0 066 186. This mail sorter includes a reading device for obtaining a zip code image or an address printed on postal matter such as letters, cards or periodical mail, a recognition unit for determining the destination of the postal matter upon recognition of the image and a sorting device for delivering the postal matter to stacking bins on sorting shelves in accordance with the destination determined by the recognition unit.
Another type of known mail handling device uses coding equipment as described, for example, in British Pat. No. GB 2 066 018. This coding equipment includes the reading device described above for obtaining images of the postal matter but does not include a recognition unit. Instead, one or more coding stations or coding devices are provided which comprise a monitor and keyboard. Successive images are displayed on the monitor so that the operator, upon watching the monitor, can input the proper zip code or area code on the keyboard.
The described coding equipment is more reliable than the formerly described sorting devices because available recognition units cannot yet get a recognition rate of 100%. When recognition units cannot recognize the zip code, the mail is rejected and delivered to a special stacking bin, which must be manually sorted at a later time. However, the disadvantage of coding equipment is that it requires more labor and can sometimes attain less performance than sorting devices with recognition units.
In recent years, with the large increase in the amount of mail, mail sorting machines that can handle large quantities of mail without much labor are desired. One proposed solution has been to install several mail sorters and operate them in parallel. However, in such a parallel system, the amount of rejected mail in each mail sorter increases and different types of rejections occur in different mail sorters. Also, over time, variations in the amount of mail handled by each sorter occur in response to the quality of zip code or address information.